TWI654313B - Method for producing active palladium (0) powder - Google Patents

Abstract

The invention relates to a method for producing palladium (0) powder, whereby the palladium (0) starting powder is subjected to heat treatment in a furnace at a temperature of not more than 370 ° C in a hydrogen atmosphere.

Description

Method for producing active palladium (0) powder

The invention relates to a method for producing active palladium (0) powder.

Powdered palladium is used in many different applications, such as as a catalyst or as an educt for conversion with a suitable reaction partner.

Palladium (0) powder (i.e., powder metal palladium in oxidation stage 0) and / or palladium (0) sponges are used to include palladium salt synthesis such as, for example, palladium (II) nitrate or palladium (II) carboxylates ( For example, the use of palladium (II) acetate or palladium (II) propionate)). During the production of palladium (II) nitrate, for example, the palladium (0) powder is converted with acetic acid and nitric acid according to the following reaction formula: 3 Pd + 6 HNO ₃ + 6HOAc → Pd ₃ (OAc) ₆ +6 NO ₂ +6 H ₂ O

To make the process efficient, it is desirable that the reaction has been initiated at relatively low temperatures (already at room temperature) and that the starting mixture does not require additional external heating or is at least minimized. For this purpose, however, this reaction requires a sufficiently high activity of the palladium (0) powder.

It is generally known that palladium (0) powder can be obtained by various production methods.

Palladium (0) powder can be produced by, for example, thermal decomposition of diamine dichloropalladium (II). Palladium (0) powder can also be obtained by reducing hexa or tetrachloropalladate with formic acid.

In addition, it is generally known to reduce a halogen-containing palladium compound to palladium by hydrazine. Thus, for example, DE 102 49 521 describes a method for producing palladium in which a halogen-containing palladium compound is reduced to palladium (0) powder by hydrazine and / or its derivative, and the palladium (0) powder thus obtained is It is heated to a temperature of 550 ° C to 1,200 ° C under a nitrogen atmosphere.

However, it is clear that the palladium (0) powder produced according to the conventional method is not sufficiently active during the production of palladium salts such as, for example, palladium (II) nitrate or palladium (II) carboxylate, at relatively low temperatures ( The reaction is preferably initiated at room temperature).

Therefore, one object of the present invention is to provide palladium (0) powder including the highest possible activity, especially for producing palladium salts.

This objective is met by a method for producing palladium (0) powder, in which the palladium (0) starting powder is subjected to heat treatment in a furnace at a temperature of not more than 370 ° C in a hydrogen atmosphere.

As will be described in more detail below, it should be noted (unexpectedly) that, in the context of the present invention, when processing Pd starting powders in a hydrogen atmosphere, a relatively low temperature (370 ° C. or lower) is sufficient to obtain Very active palladium (0) powder. The palladium (0) powder can be used to initiate a conversion reaction that has resulted in a palladium salt such as, for example, palladium (II) nitrate or a palladium (II) carboxylate at room temperature. It should also be noted (unexpectedly) that in the context of the present invention, the key to maintaining the activity at this relatively low processing temperature and that thermal hydrogenation at temperatures above 370 ° C results in significantly lower activity palladium (0) powder .

The heat treatment temperature is shown in the furnace internal temperature.

The term "palladium (0)" means that the oxidation number of palladium is 0, that is, metal palladium.

In the context of the present invention, the term "palladium (0) powder" may also include a palladium (0) sponge. As known to those skilled in the art, palladium sponges are relatively coarse-grained forms of palladium. In the context of the present invention, powder can also be understood as a material, in which powder particles are at least partially sintered together and thus the material is granular, but is no longer or only partly castable or flowable.

Those skilled in the art know methods for producing palladium (0) starting powders.

The palladium (0) starting powder can be obtained, for example, by reducing a Pd (II) compound or a Pd (IV) compound. Preferably, this concerns halogen-containing Pd (II) or Pd (IV) compounds such as, for example, PdCl ₂ , (NH ₄ ) ₂ PdCl ₆ , (NH ₄ ) ₂ PdCl ₄ , Pd (NH ₃ ) ₄ Cl _2. Pd (NH ₃ ) ₂ Cl ₂ .

Hydrazine, Salts, organic hydrazine derivatives, or formic acid may be specified as exemplary reducing agents. The production of palladium by using hydrazine as a reducing agent is described, for example, in DE 102 49 521 A1.

The palladium (0) starting powder can also be produced by, for example, thermal decomposition of diamine dichloropalladium (II).

As an option, the palladium (0) starting powder may be dried first and then subjected to thermal hydrogen treatment in an oven. This drying step can be performed, for example, in or just outside the furnace. In principle, it is also feasible to subject the still moist palladium (0) starting powder to a thermal hydrogen treatment.

As mentioned above, the heat treatment of the palladium (0) starting powder is performed in a furnace in a hydrogen atmosphere.

In order to perform the heat treatment, the palladium (0) starting powder is preferably introduced into the furnace and the hydrogen system is allowed to flow into the furnace, so that the palladium (0) starting powder exists in a hydrogen atmosphere.

In the context of the present invention, a furnace is to be understood as a device comprising a space surrounded by one or more walls, such as (inside a furnace) where heat can be applied in a controlled manner to an object to be subjected to a heat treatment.

Suitable furnaces for such heat treatments are generally known to those skilled in the art. Furnace heating can be controlled and inspected with appropriate control technology. Preferably, the measuring element for measuring the temperature is properly attached so that the temperature inside the furnace can be reliably measured and thus the risk of overheating can be reduced. A tubular furnace is mentioned herein as an exemplary furnace. However, other types of furnaces are equally suitable.

In principle, the hydrogen content of the hydrogen atmosphere can be varied within a wide range. At lower hydrogen contents, it may be necessary to choose a longer duration of treatment of the palladium (0) starting powder in a hydrogen atmosphere to make the palladium (0) powder significantly active (eg, using an inorganic acid for subsequent conversion). Relative to the total amount of gas present in the hydrogen atmosphere, the hydrogen content of the hydrogen atmosphere (ie, the hydrogen content in the furnace) is, for example, at least 5 vol%, more preferably at least 10 vol% or at least 20 vol%, or even more It is preferably at least 30% by volume or at least 50% by volume, and even more preferably at least 70% by volume or even at least 90% by volume. If provided by the presence of other gases, such as it may be (e.g.) an inert auxiliary gas (e.g., N ₂₎ or unavoidable residual amount of air. Relative to the total amount of gas present in the hydrogen atmosphere, the oxygen content (for example, in the air still present) is preferably kept as small as possible, for example, less than 1% by volume, more preferably less than 0.1% by volume or even less than 0.01% by volume.

The flow of hydrogen into the furnace may be continuous, or otherwise discontinuous. Preferably, the continuous hydrogen flow in the furnace is evident during the entire heat treatment of the palladium (0) starting powder. However, it will be explained later that it is preferred to stop supplying hydrogen to the furnace during the cooling phase of the furnace after completion of the heat treatment, and instead to supply the furnace with an inert gas such as, for example, nitrogen during the cooling phase.

Although the temperature must not exceed 370 ° C, once the hydrogen atmosphere is established in the furnace, the furnace temperature will rise.

As already mentioned above, if the hydrogen treatment of the palladium (0) starting powder is performed above 370 ° C, the activity of the palladium (0) powder will be significantly reduced in the production process of the palladium salt.

Those skilled in the art generally know appropriate measures to prevent the furnace from overheating, such as by operating one or more temperature ramps. The operating temperature ramp involves heating the furnace to a holding temperature T ₁ and maintaining the holding temperature T ₁ (as constant as possible) for a period of time t ₁ . If the second temperature ramp is also operated, there is another heating process from the first holding temperature T ₁ to the second holding temperature T ₂ and then the second holding temperature T _{2 is} maintained (as constant as possible) for a period of time t ₂ . Operating these temperature ramps makes it possible to approach the maximum temperature given by the furnace in a suitable way, thus minimizing the risk of overheating. Skilled in the art and may be readily selected as appropriate number of temperature ramp, a suitable holding temperature T _1, T _2, etc., and an appropriate holding time t _1, t _2, so as to prevent overheating of the furnace to a temperature greater than 380 ℃. For example, 3 to 10 or 4 to 8 temperature ramps can be run to heat the furnace to the maximum temperature at the same time, where the holding temperatures T ₁ , T _2, etc. may differ from each other by 10 ° C. to 100 ° C. and the holding times t ₁ , t _2, etc. 5 to 90 minutes or 15 to 80 minutes.

Alternatively, or in addition to using a temperature ramp, the risk of overheating can be minimized by a low heating rate.

Preferably, the hot hydrogen treatment in the furnace is performed at a temperature of not more than 360 ° C, preferably not more than 350 ° C.

The preferred lower temperature limit for hot hydrogen treatment in a furnace is 150 ° C, more preferably 230 ° C, and More preferably 280 ° C.

Therefore, the heat treatment of the palladium (0) starting powder is preferably performed at a temperature ranging from 150 ° C to 370 ° C, and more preferably at a temperature ranging from 230 ° C to 360 ° C or from 280 ° C to 350 ° C.

The duration of the heat treatment of the palladium (0) starting powder in a hydrogen atmosphere can vary over a wide range and also depends on the amount of palladium (0) starting powder used. The duration of the heat treatment can be appropriately selected so that the palladium (0) powder thus obtained has a sufficiently high activity in the method for producing a palladium salt. Since the activity of the palladium (0) powder from which the palladium salt is produced can be easily tested (for example, by small-scale test reactions or by thermogravimetric analysis of Pd (0) powder), the onset of Pd (0) can be easily determined Optimal time period for heat treatment of powder.

After the heat treatment, the furnace is allowed to cool (eg, to room temperature) and then the palladium (0) powder can be removed and used to produce a palladium salt. Preferably, the amount of hydrogen is no longer supplied into the furnace during the cooling process, but an inert gas, such as, for example, nitrogen or an inert gas, is supplied into the furnace.

After cooling the furnace, the palladium (0) powder may be subjected to additional post-treatments, such as mechanical pulverization and / or grinding.

If the palladium (0) powder is not immediately used to produce a palladium salt, it is advantageous to store the palladium (0) powder under an inert gas atmosphere (for example, an N ₂ atmosphere).

In another aspect, the invention relates to a system and / or a palladium (0) powder obtainable according to the method described above.

As should be described in more detail below, the palladium (0) powder produced according to the method of the present invention not only shows improved activity in producing palladium salts, but also has an additional mass increase when heated and / or annealed while exposed to air. Features that make it different from other palladium (0) powders.

In another aspect, the present invention therefore relates to palladium (0) powder that includes at least a 13.0% weight increase in mass when heated to a temperature up to 990 ° C while exposed to air.

The increase in mass can be determined by thermogravimetry. The heating rate is, for example, 10 ° C / min. The palladium (0) powder is heated from the starting temperature (which is usually 25 ° C) to a temperature up to 900 ° C and measured here The quality of the temperature interval is increased. Thermogravimetry is performed in an air atmosphere.

Preferably, the mass increase is at least 13.5% by weight, more preferably at least 14.0% by weight.

The use of this mass-increasing feature of the palladium (0) powder according to the present invention allows the thermogravimetric analysis to be used to very quickly determine whether a particular palladium (0) powder exhibits sufficiently high activity to produce a palladium salt.

In another aspect, the present invention relates to the use of the above-mentioned palladium (0) powder as an educt for producing a palladium salt.

The palladium salt may be a palladium (II) salt or a palladium (IV) salt.

Exemplary salt-based palladium salts of inorganic acids (e.g., Pd (II) nitrate, Pd (II) sulfate, or Pd (II) chloride) and palladium (II) of carboxylic acids (e.g., C _2-8 carboxylic acids) ) Salts (such as, for example, palladium acetate or palladium propionate).

In yet another aspect, the present invention relates to a method for producing a palladium salt, which comprises: (i) providing a palladium (0) powder according to the above method, and (ii) reacting the palladium (0) powder with an inorganic acid.

As mentioned above, the palladium salt may be a palladium (II) salt or a palladium (IV) salt. For exemplary salts, reference is made to the explanations given above.

Step (i) involves palladium (0) powder provided according to the method described above.

Step (ii) involves converting a palladium (0) powder with an inorganic acid. Those skilled in the art know suitable reaction conditions for converting palladium (0) powders with inorganic acids. Suitable inorganic acids include, for example, nitric acid, sulfuric acid, hydrochloric acid, or a mixture of at least two such inorganic acids (for example, a mixture of nitric acid and hydrochloric acid). The nitric acid is preferably an inorganic acid.

A preferred embodiment is a method for producing palladium (II) nitrate, wherein the palladium (0) powder is converted with nitric acid in step (ii). Palladium (II) nitrate can be used for further conversion by replacing the nitrate with another anion, for example to produce additional salts.

Also within the scope of the present invention, it is possible to have at least one other reaction partner in step (ii) in addition to the inorganic acid (for example, nitric acid). In a preferred embodiment, in step (ii), Conversion is performed in the presence of a carboxylic acid or carboxylic anhydride or a mixture thereof. Palladium (II) carboxylate can be produced in this way.

Preferably, the palladium (II) carboxylate is a palladium (II) C _2-8 carboxylate, such as, for example, palladium acetate or palladium propionate. Therefore, the carboxylic acid is preferably a C _2-8 carboxylic acid such as, for example, acetic acid or propionic acid. The anhydrides of these carboxylic acids may also be present in step (ii).

In a preferred embodiment, the inorganic acid is nitric acid and the carboxylic acid is acetic acid. Due to the presence of the reaction partners in step (ii), palladium (II) acetate is obtained.

Those skilled in the art know suitable reaction conditions for converting palladium (0) powders with inorganic acids (such as, for example, nitric acid) and carboxylic acids (such as, for example, acetic acid).

If the palladium (0) powder of the present invention is used, the reaction has been initiated at a relatively low temperature, for example, it has been initiated at room temperature.

If applicable, the starting mixture containing the educt can be heated slightly to start the reaction.

The present invention will be explained in more detail based on the following examples.

Examples

The same palladium (0) starting powder was used in all the following experiments and was produced according to the example of DE 102 49 521 A1 as follows.

Transfer Pd (NH ₃ ) ₂ Cl ₂ to a beaker and add hot deionized water until the suspension is easily stirred. Then 5 to 10 mL of ammonia solution (25% solution) was added while stirring, resulting in a slightly alkaline solution. Then, 30 to 60 mL of a hydrazine solution (22% solution) was slowly added in aliquots. The suspension will foam during the addition of hydrazine, and the addition of hydrazine must be suitable for the foaming situation. An additional 3 mL of hydrazine solution was added in excess. Subsequently, stirring was continued for more than one hour and the Pd sponge thus produced, and then filtered through a funnel filter. Rinse the Pd sponge approximately 10 times with hot deionized water. The Pd sponge, which was still slightly wet, was transferred to a quartz glass boat and pushed into a closable tube furnace. The furnace is equipped with an inner tube made of quartz glass. Subsequently, nitrogen was supplied through the inner tube. Connect the outlet of the tube to a 2n sulfuric acid gas purge bottle. After 10 minutes, the oxygen was completely removed from the inner tube, and the temperature of the furnace was heated to a temperature of 250 ° C. in a linear manner over the course of two hours. This temperature was maintained for 4 hours and then the furnace was further heated in a linear manner to a temperature of 600 ° C to 650 ° C. After a hold time of 5 hours, the furnace was allowed to cool to approximately 50 ° C while flushing with nitrogen. The Pd sponge was removed and comminuted mechanically.

Reference example 1

The palladium (0) starting powder produced according to the above method was tested for its activity for producing palladium acetate. The procedure is as follows: 30 mL of acetic anhydride and 300 mL of acetic acid are added to 30 g of palladium (0) starting powder. Then, nitric acid was added.

At room temperature, NO _x and palladium (0) powders did not react with acetic acid and nitric acid to form palladium acetate. The reaction could not be started even by heating to 60 ° C.

Example 1

The palladium (0) starting powder was placed in a tube furnace and hydrogen was allowed to flow into the furnace. The H ₂ flow rate is 2 m ³ / h. After the hydrogen atmosphere was formed, the furnace was heated to a maximum temperature of 340 ° C according to the following temperature program: heated to 100 ° C; maintained at 100 ° C for 60 minutes (first temperature ramp); further heated to 150 ° C; maintained at 150 ° C for 30 Minutes (second temperature ramp); further heating to 200 ° C; maintaining temperature at 200 ° C for 30 minutes (third temperature ramp); further heating to 280 ° C; maintaining temperature at 280 ° C for 30 minutes (fourth temperature ramp); further heating To 300 ° C; hold the temperature at 300 ° C for 30 minutes (fifth temperature ramp); further heat to 340 ° C and continue heat treatment for another 150 minutes; allow the furnace to cool to room temperature.

During the cooling phase, the H ₂ flow was stopped and replaced with nitrogen supply to the furnace.

A part of the palladium (0) powder thus obtained was subjected to thermogravimetric analysis (TG apparatus: Netzsch TG 209). The heating rate is 10 ° C / min and the sample is heated to a temperature of up to 990 ° C in an air atmosphere. The sample showed an increase of 14.2% by weight in mass.

A second sample of palladium (0) powder was taken and also subjected to thermogravimetric analysis under the same conditions. This sample showed an increase of 14.1% by weight in mass.

The remaining palladium (0) starting powder was tested for its activity in producing palladium acetate. For this purpose, the procedure of Reference Example 1 was used, that is, 30 mL of acetic anhydride and 300 mL of acetic acid were added to 30 g of palladium (0) starting powder. Then, nitric acid was added.

Even in the case of external heating without formation of some NO _x, and palladium (0) powder and acetic acid, and nitric acid react to form palladium acetate. This confirms that the palladium (0) powder of the present invention has extremely high activity.

Reference example 2

The palladium (0) starting powder was placed in a tube furnace and hydrogen was allowed to flow into the furnace. The H ₂ flow rate is 2 m ³ / h. After the hydrogen atmosphere was formed, the furnace was heated to a maximum temperature of 380 ° C according to the following temperature program: heated to 100 ° C; maintained at 100 ° C for 60 minutes (first temperature ramp); further heated to 150 ° C; maintained at 150 ° C for 30 Minutes (second temperature ramp); further heating to 200 ° C; maintaining temperature at 200 ° C for 30 minutes (third temperature ramp); further heating to 280 ° C; maintaining temperature at 280 ° C for 30 minutes (fourth temperature ramp); further heating To 300 ° C; hold the temperature at 300 ° C for 30 minutes (fifth temperature ramp); further heat to 380 ° C and continue heat treatment for another 150 minutes; allow the furnace to cool to room temperature.

During the cooling phase, the H ₂ flow was stopped and replaced with nitrogen supply to the furnace.

A part of the palladium (0) powder thus obtained was subjected to thermogravimetric analysis (TG apparatus: Netzsch TG 209). The heating rate is 10 ° C / min and the sample is heated to a temperature of up to 990 ° C in an air atmosphere. This sample showed an increase in mass of 11.9% by weight.

The remaining palladium (0) starting powder was tested for its activity in producing palladium acetate. For this purpose, the procedure of Reference Example 1 and Example 1 was used, that is, 30 mL of acetic anhydride and 300 mL of acetic acid were added to 30 g of palladium (0) starting powder. Then, nitric acid was added.

In an additional external heating only at about 80 deg.] C to form the case of NO _x, and palladium (0) powder reacts with nitric acid to form acetic acid and palladium acetate.

Claims (11)

A method for producing palladium (0) powder, wherein the palladium (0) starting powder is subjected to heat treatment in a furnace in a temperature range of 230 to 370 ° C in a hydrogen atmosphere. The method of claim 1, wherein the palladium (0) starting powder is obtained by reducing a Pd (II) compound or a Pd (IV) compound. The method of claim 1 or 2, wherein the hydrogen content of the hydrogen atmosphere is at least 5% by volume relative to the total amount of gas present in the hydrogen atmosphere. The method of claim 1 or 2, wherein the hydrogen atmosphere is generated by continuously supplying hydrogen to the furnace. The method of claim 1 or 2, wherein the furnace is heated and the heating of the furnace is interrupted by one or more temperature ramps. A palladium (0) powder obtainable by a method as claimed in any one of claims 1 to 5. A palladium (0) powder comprising at least 13.0% by weight increase in mass when heated to a temperature of up to 990 ° C while exposed to air. A use of palladium (0) powder as claimed in claim 6 or 7 as an educt for producing palladium salts. A method for producing a palladium salt, comprising: (i) providing a palladium (0) powder by a method according to any one of claims 1 to 5; (ii) converting the palladium (0) powder with an inorganic acid. The method according to claim 9, wherein the inorganic acid is nitric acid, sulfuric acid, hydrochloric acid or a mixture of at least two of these inorganic acids. The method of claim 9 or 10, wherein the conversion in step (ii) is performed in the presence of a carboxylic acid or a carboxylic anhydride or a mixture thereof.